This invention relates to multi-speed planetary transmissions for use in vehicles and more particularly to multi-speed planetary transmissions having six or more forward speed ratios.
Passenger vehicles include a powertrain that is comprised of an engine, multi-speed transmission and a differential or final drive. The multi-speed transmission increases the overall operating range of the vehicle by permitting the engine to operate through its torque range a number of times. The number of forward speed ratios that are available in the transmission determines the number of times the engine torque range is repeated. Early automatic transmissions had two speed ranges. This severely limited the overall speed range of the vehicle and therefore required a relatively large engine that could produce a wide speed and torque range. This resulted in the engine operating at a specific fuel consumption point, during cruising, other than the most efficient point. Therefore, manually shifted (countershaft) transmissions were the most popular.
With the advent of three and four speed automatic transmissions, the automatic shifting (planetary gear) transmission increased in popularity with the motoring public. These transmissions improve the operating performance and fuel economy of the vehicle. The increased number of speed ratios reduces the step size between ratios and therefore improves the shift quality of the transmission by making the ratio interchanges substantially imperceptible to the operator under normal vehicle acceleration. It has been suggested that the number of forward speed ratios be increased to five and even six speeds. This has been accomplished in many heavy truck powertrains. Six speed transmissions are disclosed in U.S. Pat. No. 4,070,927 issued to Polak on Jan. 31, 1978; U.S. Pat. No. 6,071,208 issued to Koivunen on Jun. 6, 2000, and U.S. Pat. No. 5,106,352 issued to Lepelletier on Apr. 21, 1992.
Six speed transmissions offer several advantages over four and five speed transmissions, including improved vehicle acceleration and improved fuel economy. While many trucks employ power transmissions, such as Polak, having six or more forward gear ratios, passenger cars are still manufactured with three and four speed automatic transmissions and relatively few five or six speed devices due to the size and complexity of these transmissions. The Polak transmission provides six forward speed ratios with three planetary gear sets, two clutches and three brakes. The Koivunen patent utilizes six torque transmitting devices including four brakes and two clutches to establish the six forward speed ratios and another reverse speed ratio. The Lepelletier employs three planetary gear sets, three clutches and two brakes to provide six forward speeds. One of the planetary gear sets is positioned and operated to establish two fixed speed input members for the remaining planetary gear sets.
It is an object of the present invention to provide an improved multi-speed transmission family wherein each family member has at least six forward speed ratios and one reverse speed ratio.
In one aspect of the present invention, the multi-speed transmissions have three planetary gear sets and five rotating torque transmitting mechanisms (clutches). In another aspect of the present invention each planetary gear set has three members comprised of a sun gear member, a ring gear member, and a planet carrier assembly member. In yet another aspect of the present invention, the first members of the first and second planetary gear sets are continuously interconnected by a first interconnecting member. In still another aspect of the present invention, the second members of the first and second planetary gear sets are continuously interconnected and also continuously connected with a stationary member of the transmission such as a housing by a second interconnecting member. In yet still another aspect of the present invention, an input shaft is continuously connected to one member of the third planetary gear set, and an output shaft is continuously connected with another member of the third planetary gear set. In yet still another aspect of the present invention each of the planetary gear sets have one non-continuously connected member.
In a further aspect of the present invention, the five torque transmitting mechanisms are selectively connectable in combinations of two to establish at least six forward speed ratios and one reverse speed ratio in the planetary gear sets between the input shaft and output shaft. A first of the torque transmitting mechanisms is selectively connectable between the third member of the first planetary gear set and a member of the third planetary gear set which may also be connected with the input shaft or the output shaft. In a yet further aspect of the present invention, a second of the torque transmitting mechanisms is selectively connectable between the first interconnecting member and a member of the third planetary gear set which may also be the member connected with the input shaft or the output shaft. In still a further aspect of the present invention, a third of the torque transmitting mechanisms is selectively connectable between one member of the third planetary gear set and one of the members of the first planetary gear set or the second planetary gear set. In a yet still further aspect of the present invention a fourth of the torque transmitting mechanisms is selectively connectable between the non-continuously connected member of the first planetary gear set or the second planetary gear set and a member of the third planetary gear set. In a yet still further aspect of the present invention, a fifth of the torque transmitting mechanisms is selectively connectable between one of the non-continuously connected members of the first planetary gear set or the second planetary gear set and a member of the third planetary gear set.